Television receiver with transistorized video amplifier



May 28, 1963 A. w. MAssMAN TELEVISION RECEIVER WITH TRANSISTORIZED VIDEOAMPLIFIER Filed Feb. 27, 1961 Unite The present invention relatesgenerally to amplifiers, and it relates more particularly to an improvedtransistorized video amplifier for use in a television receiver.

As is well known, the present-day television signal is standardized toinclude fan amplitude modulated video carrier and a frequency modulatedsound carrier, these carriers being frequency displaced from oneanother. Both the video carrier and the sound carrier are amplified in acommon radio frequency amplifier and in `a common intermediate frequencyamplifier of the television receiver, and both carriers ,are detected ina video detector of the receiver. The video detector produces videosignals extending through a particular frequency range, and it alsoproduces yan inter-carrier sound signal which is displaced in frequencyfrom the frequency range of the detected video signals and which isfrequency modulated by the audio intelligence.

The detected video signals from the video detector are amplified in thevideo amplifier, and they are applied to the picture tube `of thetelevision receiver to control the intensity of the cathode-ray beamtherein in accord-ance with the video intelligence. The frequencymodulated inter-carrier sound signal is introduced -t-o the audiochannel of the receiver for subsequent amplification and reproductiontof the sound intelligence.

An object of the present invention is to provide a transistorized stagein a television receiver which functions efficiently tto pass thedetected video signals to the video channel of the television receiverfor subsequent video reproduction, and which also serves in an improvedmanner to pass the inter-carrier sound signal to the audio channel ofthe television receiver for subsequent sound reproduction.

A more general object of the invention is to provide an amplifier whichis capable of responding to frequency displaced signal-s, and ofefficiently and selectively introducing the signals to individual outputchannels.

Another object of the invention is to provide a transistorizedlamplifier stage for use in ta television receiver and which is capableof efficiently directing the inter-carrier sound signal to the soundchannel of the receiver and the video signals tothe video channel 'ofthe receiver, and 4which amplifier is simple in its construction so asto be practically and commercially feasible.

A feature of the invention is the provision of an improvedItransistorized video Iamplifier adapted to be intercoupled between thevideo detector and video output amplifier of a television receiver `andwhich functions las an impedance matching network in the frequency rangeof the detected video signals so as to provide lan eficien-t couplingfrom the video detector to the video output arnplifier; and which isfurther coupled to the sound intermediate frequency tamplifier of thetelevision receiver to function as a selective amplifier `at thefrequency of the inter-carrier sound signal, -so that the inter-carriersound signal may be introduced in amplified form to the sound channel ofthe television receiver.

A fur-ther feature of the invention is the provision of such an improvedtransistorized video amplifier which presents a relatively highimpedance to the video detector of the television receiver so as toobviate excessive loading of the video detector, and which presents arelatively low States Patent ice output impedance to drive the videooutput stage of the television receiver.

The above and other features of the invention which are believed to benew are set forth with particularity in the claims. The inventionitself, however, may be best understood by reference to the followingdescription in conjunction with the accompanying drawing in which thesingle FIGURE represents a television receiver, partly in block form andpartly in circuitry, the receiver including an improved transistorizedvideo amplifier constructed in accordance with the concepts of thepresent invention, `and representing an embodiment of the invention.

The television receiver illustrated in the accompanying drawing includesya radio frequency amplifier `lil Which may have one or more stages, andwhich may be constructed in known manner. The radio frequency arnplifierV10 has input terminals connected to a suitable antenna 12, and it hasoutput terminals coupled to a first detector 14. The first detector11imay also be of usual construction, and -it is coupled to anintermediate f-requency amplifier lo. The intermediate frequencyainplifier lo may have Ione or more stages.

The intermediate frequency amplifier `1.6 is coupled through a couplingtransformer 18 to the video detector Ztl of the receiver. The videodetector includes a diode 22 and associated circuitry. The associatedcircuitry includes a load resisto-r 24 `and an inductance coil 26connected in series across the output terminals of the derector circuit.The resistor 24- may have a resistance, for example, of 5.6 kilo-ohms,and the inductance coil 26 may have an inductance of 8.5 mircohenries.The inductance coil 2o is connected to a resistor 28 which is shunted bya capacitor Btl. The resistor 2S is connected to Aa point of referencepotential, such as ground, and it may have a resistance of l kilo-ohm.The capacitor 3) may have a capacity of .00d microfarad, for example.

The resistor 24 is connected to the base electrode of a PNP transistorSil, and the junction of the inductance coil 26 and resistor 2S isconnected through a pair of resistors `32 and 34 to the emitter of thetransistor 30. The resistor 32 may have a resistance of 22()l ohms, forexample, and the resistor 34 may have a resistance of 5 60 ohms. Thejunction of the resistors 32 and 34 is connected to the positiveterminal BJ,- of an appropriate source of unidirectional potential, thenegative terminal of the source being connected to a point of referencepotenti-al, such as ground.

The transistor 3) is connected as a first video amplifier fo-r thetelevision receiver, and this video amplifier is constructed in`accordance with the concepts of one embodiment of the presentinvention. The collector of the transistor 3ft is connected to acapacitor 36 and to a capaci-tor 37. The capacitor 36 may have -acapacity of .O'l microfarad, for example; and it is shunted by aresistor 4t) which may, for example, have a lresistance of 680 ohms.'ilhe capacitor 37 is connected to the point of reference potential, andit may have a capacity of i8 micromicrofa-rads, for example. v

The capacitor 36 is coupled through an inductance coil B to one side ofa parallel resonant network 42. The inductance coil 38 may have aninductance of 6 microhenries, for example. The resonant network 42includes a capacitor shunted across an inductance coil, a selected tapon the inductance coil being connected to the point of referencepotential, such as ground, andthe inductance coil forming the primary ofa coupling transformer 44.

The secondary of the coupling transformer 44 is coupled through aresistor 46 to the base of a PNP transistor 48. The resistor 46 may havea resistance of 22 ohms, for example. The transistor 48 is connected asan audio intermediate frequency amplifier for the television receiver.The other side of the secondary of the transformer 44 is connected tothe junction of a pair of resistors Si) and 52. The resistor 50 may havea resistance of 2.7 kilo-ohms, -for example, and it is connected to thepositive terminal B+ of the source of unidirectional potential. Theresistor 52 may have a resistance of l kilo-ohm, and it is connected tothe Ipoint of reference potential.

The junction of the resistors Sil and 52 is connected through acapacitor 54 to the emitter of the transistor 48, and the emitter isconnected through a resistor 56 to the positive terminal B+. Thecapacitor 54 may have a capacity of .Ol microfarads, for example, andthe resistor 56 may have a resistance of 3.3 kilo-ohms. l

The collector of the transistor 48 is connected through a resistor 58 toa tuned output circuit 60, and the output circuit is coupled to thesound channel 62 of the receiver. The sound channel 62 may include theusual audio detector, driver and output stages, and it is coupled to ausual sound reproducer 64.

The emitter of the transistor 30 in the first video amplifier is coupledthrough an inductance coil 7@ to the base of a PNP transistor 72. Thelatter transistor is included in the video output stage of the receiver,and its base is connected to a capacitor 74. The coil 70 may have aninductance of 6 microhenries, and the capacitor 74 may have a capacityof 33 micromicrofarads, this capacitor being connected to the point ofreference potential. The emitter is also connected to a series resonantnetwork including an inductance coil 76 and a series connected capacitor78. The inductance coil may have an inductance of 2.1 microhenries, andthe capacitor may have a capacity of S2 micromicrofarads, the capacitorbeing connected to the point of reference potential, such as ground.

The emitter of the transistor 72 is connected through a resistor 80 to acapacitor 82. The resistor Sti may have a resistance of 47 ohms, forexample, and the capacitor 82 may have a capacity of 500 microfarads.The capacitor 82 is connected to the point of reference potential. Thejunction of the resistor 8f) and the capacitor 82 is connected to vtheslider of a contrast control 86, an auxiliary contrast control 88 and anautomatic gain control potentiometer 90. The collector of the transistor72 is connected through a peaking network 92, and through a couplingcapacitor 94 to the cathode of the picture tube 96 of the receiver.

Other usual circuitry is included in the coupling between the transistor72 and the picture tube which forms no part of the present invention.The sweep and synchronizing portions of the television receiver,likewise, form no part of the present invention and have not been shown.

When the television receiver is tuned to a particular television signal,the signal is intercepted by the antenna 12 and amplified by the radiofrequency amplifier 10. The amplifie-d radio frequency signal from theamplifier is heterodyned by the first detector 14 to the selectedintermediate frequency of the receiver. The resulting intermediatefrequency signal is amplified by the intermediate frequency amplifier 16and is introduced to the video detector 20 for detection. The videodetector produces across its load resistor 24 the `detected videosignals, and it also produces the frequency modulated 4.5 megacycleinter-carrier sound signal. These signals are passed by the first videoamplifier 30 in a manner to be described. The first video amplifierintroduces the intercarrier sound signal to the audio intermediatefrequency amplifier of the transistor 48 for amplification, and forsubsequent detection and reproduction in the sound channel 62. Theamplifier 30 also passes the detected video signals to the video outputamplifier of the transistor 72 for amplification and for introduction tothe cathode of the picture tube 96.

The resistors 28 and 32 serve as a voltage divider to provide the properforward bias for the transistor 30 in the first video amplifier. Theinductance coil 95 and capacitor 96 serve as a by-pass for theintermediate frequency signals and prevent these signals from reachingthe video circuits; and these elements also prevent harmonies of thesesignals from reaching the input circuit which would cause interferencepatterns.

The first video amplifier 39, in accordance -with the invention,performs a dual function. in the frequency range of the detected videosignals, for example, the collector circuit of the transistor 39 ismaintained essentially at the potential of the point of referencepotential. This is achieved by the tuned circuit 42. This tuned circuitis a parallel resonant circuit, and it is tuned to the frequency of theinter-carrier sound signal, that is, to 4.5 megacycles. At the frequencyof the video signals, the resonant network 42 presents a relatively lowimpedance to the point of reference potential, so that the collector ofthe transistor 36 is maintained essentially at the potential of thepoint of reference potential in the frequency range of the videosignals.

The series-resonant circuit 76, 73 is also tuned to the 4.5 megacyclefrequency of the inter-carrier sound signal. The series-resonant circuitformed lby the inductance coil 70 and capacitor 74 filters any IF signalthat can `cause interference with the demodulated signal.

Therefore, in the frequency range of the detected video signals, thefirst video amplifier of the transistor St) functions as a commoncollector amplifier, and it exhibits characteristics similar to acathode follower. That is, the first video amplifier serves to introducethe detected video signals to the vi-deo output amplifier 72 to theexclusion of the inter-carrier sound signal; and it also serves topresent a high impedance to the second detector so as to preventexcessive loading of the second detector, and to present a low outputdriving impedance for the video output amplifier 72.

At the 4.5 megacycle frequency of the inter-carrier sound signal, on theother hand, the first video amplifier 30 functions as a common emitteramplifier. At that frequency, the traps 76, 78 present a relatively lowimpedance so that the emitter of the transistor 30 is established and issubstantially the potential of t-he reference potential point. Theinter-carrier sound signal is, therefore, amplified by the first videoamplifier and applied through its collector circuit to the sound channelof the receiver, to the exclusion of the video signals.

The invention provides, therefore, an improved video amplifier whichserves a dual function, efiiciently to separate and amplify theinter-carrier sound signal from the detected video signals to introducethe sound signal in amplified form to the sound channel of the receiver;and also to separate the video signals from the inter-carrier soundsignal, and to provide an impedance matching network for the videofrequency signals between the video detector and the video outputamplifier of the receiver.

What is claimed is:

l. In a television receiver for utilizing a television signal having avideo carrier amplitude modulated by video signals and a sound carrierfrequency displaced from said video carrier and frequency modulated byaudio signals, which television receiver includes a detector forproducing detected video signals in a particular frequency range and forfurther producing an inter-carrier sound signal frequency displaced fromsaid range and frequency modulated by the audio signals, and whichfurther includes an audio channel and a video channel, the combinationof: a video amplifier coupled to said detector and including atransistor having a first electrode coupled to said detector and ftutherhaving a second electrode and a third electrode, first circuit meanscoupling said second electrode to said audio channel and `includingresonant network means coupled to a point of reference potential forestablishing said second electrode substantially at the potential ofsaid lpoint of reference potential in the frequency range of said videosignals, and second circuit means coupling said third electrode to saidvideo channel and including resonant network means coupled to said pointof reference potential for establishing said third electrodesubstantially at the potential of said point of reference potential atthe 'frequency of said inter-carrier sound signal.

2. `In a television receiver for utilizing a television signal having avideo carrier amplitude modulated by audio signals and a sound carrierfrequency displaced from said video carrier yand frequency modulated byaudio signals, which includes a detector for producing detected videosignals in a particular frequency range and for further producing anintercarrier sound signal frequency displaced from said range andfrequency modulated by the audio Signals, and which further includes anaudio channel and a video channel, the combination of: a video amplifiercoupled `to said detector and including a transistor having a .baseelectrode and an emitter electrode and a collector electrode, inputcircuit means coupled to said base electrode for coupling said detector-to said video amplifier, first output circuit means coupled -to saidcollector electrode for coupling said video amplifier to the audiochannel and including resonant network means coupled to a point ofreference potential for establishing said collector electrodesubstantially at the potential of said point of reference potential inthe frequency range of said video signals, and second output circuitmeans coupled to said emitter electrode for coupling said videoamplifier `to ythe video channel and including resonant network meanscoupled to said point of reference potential for establishing saidemitter electrode substantially at the potential of said point ofreference potential at the frequency of said inter-carrier signal.

3. The combination dened in cla-im 3 and in which said resonant networkmeans in said iirst output circuit means includes a parallel resonantnetwork adapted to be tuned to the frequency of said inter-carrier soundsignal.

4. The combination defined in claim 2 and in which said resonant networkmeans in said second output circuit means includes a series resonantnetwork adapted to be tuned to the frequency of said inter-carrier soundsignal.

5. \In a television receiver for utilizing a signal having a modulatedvideo carrier and a modulated sound carrier, the combination of a videoamplifier including a transistor having rst, second and thirdelectrodes, means for applying the television signal to said firstelectrode with respect to a reference potential, circuit means connectedto said second electrode for utilizing the video carrier and including aresonant network for establishing said second electrode substantially atthe reference potential in the frequency range of the sound carrier, andfurther circuit means connected to said third electrode for utilizingthe sound carrier and including resonant network means for establishingsaid third electrode substantially at the reference potential in thefrequency r-ange of the video carrier, whereby said video amplifierperforms the dual function of separating and amplifying both the videocarrier and the sound carrier.

References Cited in the file of this patent UNITED STATES PATENTS2,853,603 Herold Sept. 23, 1958

1. IN A TELEVISION RECEIVER FOR UTILIZING A TELEVISION SIGNAL HAVING AVIDEO CARRIER AMPLITUDE MODULATED BY VIDEO SIGNALS AND A SOUND CARRIERFREQUENCY DISPLACED FROM SAID VIDEO CARRIER AND FREQUENCY MODULATED BYAUDIO SIGNALS, WHICH TELEVISION RECEIVER INCLUDES A DETECTOR FORPRODUCING DETECTED VIDEO SIGNALS IN A PARTICLUAR FREQUENCY RANGE AND FORFUTHER PRODUCING AN INTER-CARIER SOUND SIGNAL FREQUENCY DISPLACED FROMSAID RANGE AND FREQUENCY MODULATED BY THE AUDIO SIGNALS, AND WHICHFURTHER INCLUDES AN AUDIO CHANNEL AND A VIDEO CHANNEL, THE COMBINATIONOF: A VIDEO AMPLIFIER COUPLED TO SAID DETECTOR AND INCLUDING ATRANSISTOR HAVING A FIRST ELECTRODE COUPLED TO SAID DETECTOR AND FURTHERHAVING A SECOND ELECTRODE AND A THIRD ELECTRODE, FIRST CIRCUIT MEANSCOUPLING SAID SECOND ELECTRODE TO SAID AUDIO CHANNEL AND INCLUDINGRESONANT NETWORK MEANS COUPLED TO A POINT OF REFERENCE POTENTIAL FORESTABLISHING SAID SECOND ELECTRODE SUBSTANTIALLT AT THE POTENTIAL OFSAID POINT OF REFERENCE POTENTIAL IN THE FREQUENCY RANGE OF SAID VIDEOSIGNALS, AND SECOND CIRCUIT MEANS COUPLING SAID THIRD ELECTRODE TO SAIDVIDEO CHANNEL AND INCLUDING RESONANT NETWORK MEANS COUPLED TO SAID POINTOF REFERENCE POTENTIAL FOR ESTABLISHING SAID THIRD ELECTRODESUBSTANTIALLY AT THE POTENTIAL OF SAID POINT OF REFERENCE POTENTIAL ATTHE FREQUENCY OF SAID INTER-CARRIER SOUND SIGNAL.